'Proof' in the Bible

And my message and my preaching were not in persuasive words of wisdom [using clever rhetoric], but [they were delivered] in demonstration of the [Holy] Spirit [operating through me] and of [His] power [stirring the minds of the listeners and persuading them],

Am I not free [unrestrained and exempt from any obligation]? Am I not an apostle? Have I not seen Jesus our [risen] Lord [in person]? Are you not [the result and proof of] my work in the Lord?